Fluid circulation systems are used in many industries and vary among these industries. For example, fluid circulation systems find application in mechanical systems ranging from the most rudimentary machines requiring the lubrication and cooling of moving and/or rotating parts, such as small horsepower engine indoor and outdoor equipment, to more complex systems, such as those used, for example, in the automotive industry and in heavy machinery of all kinds, and further to even more complex and highly specialized military and industrial applications that are characterized by high power density. Such systems produce an uncommon amount of power in relatively small envelopes. Some principles underlying the operation of such systems are also used outside those fields where engines are generally considered, and find application, for instance, in the biomedical engineering field. The self-acting system disclosed herein may find application to any of the foregoing fields, and all others that employ such systems, and which will become apparent to one skilled in the art upon reading and understanding the disclosure provided.
Common to the foregoing systems is a moving and/or rotating part that needs continuous lubrication, reduced friction, temperature control and, in general, a means to enhance efficient and smooth movement. Also common to systems having such a moving or rotating part or parts is an external pressure source that delivers lubricant to the system, usually through an external pumping mechanism and including pipes, tubes or other forms of compatible conduit, and withdraws used lubricant from the system in the same manner. The external pressure source and attendant piping represent a cumbersome but necessary addition to the system being supported thereby, and additionally are a source of system breakdown and maintenance needs, thus representing not only an added initial expense of the system, but also an added and continuous maintenance expense. Further, for advanced, more complex systems that operate in extreme environments, or experience extreme operating conditions, i.e. high temperature and pressure, or increased rotational speeds, materials used for these external systems must also be able to withstand these extreme conditions, thereby making them even more costly to obtain, create and maintain.
Without wishing to be bound to any one operating system, and in the interest of providing a merely exemplary system to better demonstrate the pitfalls of existing systems and the advantages to such systems of the inventive self-acting fluid circulation system disclosed herein, the self-acting system will be discussed hereafter at times with reference to the application thereof to a bearing system. More particularly, in order to demonstrate the use of the self-acting system in extreme circumstances, the system may be shown and discussed hereafter with reference to systems employing high operating temperatures, in excess of 1000° C., and under conditions of increased rotational speeds, in excess of 16,000 rpm and as high as 30,000-100,000 rpms. Due to these conditions and parameters, the exemplary system further includes the use of a liquid metal lubricant for reasons which will become apparent in the following disclosure. Notwithstanding the foregoing, it is to be understood that the usage and functionality of the inventive system is in no way limited to the use of liquid metal lubricants or use of the system under extreme conditions, but can be used with any suitable lubricant or fluid, and may further be used at any temperature ranging from ambient to the temperatures mentioned above, and even to cryogenic ranges and systems operating below ambient and under conditions attendant to such temperatures. It will be understood by the skilled artisan, in light of the full disclosure, that the self-acting, zero-leakage fluid circulating system is suitable for use in other systems and that the bearing system discussed is merely one option for its use.
As with most applications where the self-acting, zero-leakage fluid circulation system may find use, known systems, including the exemplary bearing system mentioned above, generally enjoy the use of an external pumping system. Schuller and Anderson, (F. T. Schuller and W. J. Anderson, Operation of Hydrodynamic Journal Bearings in Sodium Temperatures to 800° F. and Speeds to 12,000 rpm, NASA TN-D-3928, 1967), studied hydrodynamically lubricated bearings that used sodium as the working fluid. The bearings studied were designed for working temperatures of up to 800° F. and speeds approaching 12,000 rpm. The sodium supply for the bearing was pumped through a closed loop external circulating system. Other researchers, like Hall and Spies, (J. Hall and R. Spies, Research in the Field of Liquid Metal Lubricated Bearings, Report RDT-TDR-63-4289, Parts I, II, III, North American Aviation, 1965, Hall et al., Determination of Working Fluid Lubrication Capability in Journal Bearings, Report ASD-TDR 62-640, Parts I, II, WPAFB, 1963, R. A. Burton and Y. C. Hsu, Fundamental Investigation of Liquid Metal Lubricated Bearings, USAEC Report SWRI-1228P832, Southwest Research Institute; W. D. Richards, Hydrodynamic Journal Bearing Tests in Lithium, Report TIM-915, Pratt and Whitney, 1965, and P. M. McDonald, Lubrication Behavior of Liquid Metals, Report WADC-TR-59-764, North Carolina College, 1960) did fundamental work with regard to the use of sodium and lithium lubrication of bearings for military and space applications. As with the above systems, these latter bearing systems employed external pumping systems. As used herein, the term “external” means outside of or extraneous to the moving part of interest and its housing, and containing a pump actuated by a motor as well as piping systems leading carrying the lubricant to and from such bearings. This pump represents the source of fluid circulation and overall system pressurization.
Similarly, research has advanced with regard to bearing and seal design. See M. J. Braun, R. L. Mullen, and R. J. Hendricks, An Analysis of Temperature Effect in a Finite Journal Bearing With Spatial Tilt and Viscous Dissipation, ASLE Transactions, 47:405-411, 1984, and M. Dzodzo and M. J. Braun, Pressure and Flow Characteristics in a Shallow Hydrostatic Pocket With Rounded Pocket/Land Joints, Tribology International, Austrib Special Issue, 29, 1996, discussing the application of Reynolds-based and Navier-Stokes-based numerical algorithms to hydrodynamic and hydrostatic bearing design. This research focused on evaluating the effects of temperature, load, speed and geometry on bearing operation. While the relevant body of literature is replete with papers that address the subject of design, construction and operation of self-acting bearings, these references noticeably lack any teaching that shows a combination of such systems with the self-circulating, zero-leakage, high temperature and high rotational speed operating system provided by the inventive system disclosed herein.
The SPIRALG or SPIRALI codes developed by Walowit (J. A. Walowit, Users Manual For Computer Code Spiralg. Report NASA, Contract NAS 3-25644, 1992; and J. A. Walowit, Users Manual For Computer Code Spiralg, Gas Lubricated Spiral Grooved, Cylindrical and Face Seals. Report NASA, NASA/CR2003-212361, 2003) were tooled to simulate cylindrical and thrust spiral groove bearings and seals. These codes have reached national prominence and are presently widely used. The codes are based on the Reynolds equation and can calculate performance characteristics like load carrying capacity, leakage, stiffness and damping. The Reynolds equation is a very special form of the continuity equation that when incorporating the momentum equation provides a conservative equation that balances the external forces and the viscous forces acting on a fluid in motion, and is the fundamental equation of bearing lubrication.
In addition to the foregoing, the technology of porous bearings, but without a combination with a fluid reservoir as proposed by the inventive system disclosed herein, is well-known. This technology in fact uses an external pumping system to feed fluid through the porous medium to the bearings. See, for example, Ming-Da Chen, Kuo-Ming Chang, Jau-Wen Lin, and Wang-Long Li, Lubrication of Journal Bearings—Influence of Stress Jump Condition at the Porous-Media/Fluid Film Interface, Tribology International, 35:287-295, 2002; Abdallah A. Elsharkaway and Lotfi H. Guedouar, Hydrodynamic Lubrication of Porous Journal Bearings Using a Modified Brinkman-Extended Darcy Model, Tribology International, 34:767-777, 2001; and Jaw-Ren Lin, Chi-Chuan Hwang, and Rong-Fuh Yang, Hydrodynamic Lubrication of Long, Flexible, Porous Journal Bearings Using the Brinkman Model, Wear, 198:156-164, 1996. In classical most practiced cases, the porous medium is used as a fluid transfer medium through which an external oil supply is pumping fluid into the bearing. There are, however, low speed, low temperature systems today where it is undesirable or impractical to deliver external fluid. Such systems may be self-lubricating, however they are not porous nor do they exhibit the use of a closed loop self-circulating system per the current teaching provided herein. See Boston Bearing/Boston Gear, 2000 Catalogue. In some of these cases, as the journal moves and creates a pressure gradient, the fluid from inside the porous layer and/or channel is drawn into the fluid film, further enabling lubrication. Noticeable, however, is the lack of a means to exchange fluid between an external reservoir and the bearing space, or a means for fluid to circulate between the active space of the bearing and the passive space of the reservoir continuously as is present in the inventive system provided herein. Novel to the invention is a closed loop circulation system where fluid circulates continuously between the active and passive spaces of the bearing system without ever being removed by or to and external pumping mechanism. See also J. A. Tichy, A Porous Media Model For Thin Film Lubrication, ASME Journal of Tribology, 117:16-21, 1995, showing that a slider bearing modified to include a porous medium increases the load-carrying capability and reduces the friction coefficient.
Even though the current state of the art with regard to bearings has made some advances, there has been no effort made nor has art become available teaching one how to combine various aspects of such advances to improve bearing performance under self-circulating, zero-leakage, high temperature, high rotational speed conditions. Such a lack is in part due to the design nuances that inhibit combination of the features mentioned in a straight forward manner; i.e., combination requires a balancing of principles and design so as address inherent problems encountered in combining such systems. Bearing systems remain complicated to operate and maintain with respect to the use of pumping and piping equipment to feed and remove lubricants necessary to the efficient operation of the bearing system. In addition, current lubricant systems are not well suited for high temperature applications, beyond the working temperatures of the lubricant and the few that may find application at high operating temperatures, such as the sodium and lithium lubricants mentioned earlier, have been long ago abandoned for a variety of reasons, including environmental, technical and financial issues.
The foregoing establishes that it is known in the art to: provide a shaft and a stationary enclosure for use as a bearing system; that the stationary enclosure may be porous; that the fluid may be held in a reservoir; and that systems employing the foregoing advances are used with external pumps to provide fluid to the system. Nothing in the current state of the art, however, provides for or even suggests that a system, without an external pumping mechanism, that is a self-acting, self-circulating, no pump system that can function infinitely time-wise if leakage is substantially eliminated can be constructed. In short, the art lacks any teaching to the elimination of the external pumping mechanism while maintaining a fully functioning system that is, in addition, self-acting and self-circulating as defined herein.
What is needed is a self-acting, self-circulating fluid system, capable of moving a fluid through the system in response to a pressure gradient created within the system and without the use of an external pressure mechanism or fluid supply and removal equipment.